This invention relates to a thermally responsive switch which is suitable for disposition in automobiles so as to sense the temperature of an overheated portion in the case of an abnormal condition of a transmission or compressor recirculating a refrigerant through a heat-exchange system and so as to be responsive to the abnormal temperature to thereby open an electrical circuit to deenergize an electromagnetic clutch transmitting power to the compressor or to thereby operate a warning device in the case of the engine or transmission to be protected.
In automobiles, engine power is conventionally transmitted to a compressor of an air conditioning system through an electromagnetic clutch, thereby driving the compressor. A thermally responsive switch is employed for sensing an abnormal temperature in the overheat condition of the compressor due to the influence of the ambient temperature or reduction in the lubrication effect due to a shortage of a refrigerant, and interrupting the operation of the compressor or warning of the compressor overheat condition, thereby opening an electric circuit.
The above-described thermally responsive switch is disclosed in Japanese Published Patent Application (Kokoku) No. 40-27898, Japanese Laid-open Patent Application (Kokai) No. 62-143330 and Japanese Laid-open Utility Model Reg. Application (Kokai) No. 61-3648. In such conventional thermally responsive switches, a thermally responsive element formed of a dish-shaped bimetal, inverting its curvature with a snap action when subjected to heat or the like, rests on the inner bottom face of a housing enclosing the element or disposed in the housing with a gap between the circumference of the thermally responsive element and the inner circumferential wall of the case. The gap is so determined that inversion of the thermally responsive element is not prevented by the housing inner circumferential wall. In these conventional thermally responsive switches, unstable contact between the thermally responsive element and the housing inner face or the presence of the gap therebetween causes variations in the heat transmission. Furthermore, a relatively long thermal response period results in problems of the stability of the operating temperature. Additionally, parts employed in the conventional thermally responsive switches need a high level of accuracy and too much time in the assembly.